The present invention is related to a pneumatic tool, an more particularly to a torque restricting structure of pin hammer-type; hammering mechanism.
The hammering mechanisms of conventional pneumatic tools at least include two types. One is twin hammer-type hammering mechanism in which specifically shaped hammers are provided to hammer an anvil. The other is pin clutch-type hammering mechanism as disclosed in U.S. Pat. No. 3,174,597, in which dog pins are used to hammer an anvil. In the pin clutch-type hammering mechanism, a ridged rail is disposed on a cam sleeve. The ridged rail serves to guide two dog pins on two sides of the anvil to radially hammer the jaws projecting from two sides of the anvil in predetermined travel. An great external force is instantaneously applied to the anvil to make the same rotate.
This applicant recites in U.S. patent application Ser. No. 09/986,543 that in actual use, the above conventional twin hammer-type hammering mechanism will instantaneously output an excessively great torque which tends to damage a work piece. Reversely, in actual use of the pin clutch-type hammering mechanism, the anvil is instantaneously hammered by the dog pins and rotated. In the instant of hammering, the pin clutch-type hammering mechanism due to instantaneously excessively great output can be hardly controlled within a safety torque range. Therefore, the work piece is very likely to get damaged. According to the above, it is known that both of the twin hammer-type hammering mechanism and the pin clutch-type hammering mechanism have the same shortcoming and need to be improved.
It is therefore a primary object of the present invention to provide a torque restricting structure of pin hammer-type hammering mechanism. The torque restricting mechanism is able to restrict the torque output by the pneumatic tool within a safety range, whereby the pneumatic tool can stably output torque.
According to the above object, the torque restricting structure of pin hammer-type hammering mechanism of the present invention includes: an anvil having a shaft body, two symmetrical arched jaws projecting from the middle of the shaft body opposite to each other; two hammering pins each having a column body parallel to the shaft body of the anvil, the hammering pins being axially movable between a hammering position and a separating position, whereby when in the hammering position, a lateral face of each hammering pin hammers a lateral face of a corresponding projecting jaw and when in the separating position, the hammering pins are separated from the projecting jaws; a locating guide section; and a cam having a ridge section for abutting against the locating guide section. When the cam and the locating guide section are moved relative to each other, the cam is pushed to drive the hammering pins to move between the hammering position and the separating position. The ridge section has a ridge tip in a highest position. When the hammering pins are driven by the cam to move to the hammering position, the ridge face of the ridge section abuts against the locating guide section has not yet reached the position of the ridge tip, whereby the hammering pins have already abutted against the corresponding projecting jaws to restrict the cam from being further moving and the ridge section and the locating guide section are kept engaged with each other.
The present invention can be best understood through the following description and accompanying drawings wherein: